1. Field of the Invention
The present invention relates to an inverter device of high reliability which is of small size and excellent cooling efficiency, and a method of manufacturing the inverter device thereof and an electric automobile (sometimes called an electric vehicle or an electric car) incorporating the inverter device thereof.
2. Description of the Related Art
Miniaturization and improvement of reliability of power semiconductor elements and inverter devices employing these are being demanded. When semiconductor elements and inverter devices employing these are employed in an electric automobile, reduction in size and improved reliability are particularly important.
In order to achieve reduced size and improved reliability of power semiconductor elements and inverter devices employing these, power semiconductor elements and inverter devices are required that have excellent cooling efficiency such as Japanese Laid-Open patent 2003-153554.
The construction of a conventional inverter device is described below with reference to FIG. 1 and FIG. 2. FIG. 1 is a partial axial cross-sectional view showing the mounting structure of semiconductor chips in the interior of a power semiconductor element; FIG. 2 is a partial perspective view of a power semiconductor element.
In the inverter device shown in FIG. 2, a single arm of a three-phase inverter is constituted by connecting in parallel a plurality of IGBTs (insulated gate bipolar transistors) 171 and diodes 181 constituted by semiconductor chips of size no more than 10 mm square; furthermore, a plurality of semiconductor chips constituting a single arm of the three-phase inverter are bonded with a conductor 20 of thickness between 1.5 mm and 5 mm; the conductor 20 is adhesively fixed to a cooler 22 by a ceramics-containing insulating resin sheet 23. (“10 mm square” or “□10 mm” indicates that the length of one side of a square shape is 10 mm.)
Furthermore, in the inverter device shown in FIG. 2, four parallel-connected IGBTs 171A to 171D constituting an upper arm of the W phase of a three-phase inverter and two parallel-connected diodes 181A to 181B are arranged in a single row with an upper arm conductor 25 constituting an upper arm of the three-phase inverter; likewise, four parallel-connected IGBTs 172A to 172D constituting a lower arm of the W phase of a three-phase inverter and two parallel-connected diodes 182A to 182B are arranged in a single row with a lower arm conductor 26 constituting a lower arm of a three-phase inverter. In addition, a three-phase output conductor 27 that connects three-phase output terminal 32 with the IGBTs 171A to 171D and the diodes 181A to 181B is arranged on the upper arm conductor 25 between the upper arm conductor 25 and the lower arm conductor 26.
The construction of the upper arms and the lower arms will now be described. The arms are as follows in the case of an inverter device that converts DC current to three-phase AC current as shown in FIG. 3. Specifically, in order to generate three-phase AC power from DC battery power, an inverter is constituted comprising three-phase arms (U phase, X phase), (V phase, Y phase) and (W phase, Z phase) and conversion to AC current is effected therein. This AC current provides three-phase AC power for driving a three-phase motor.
The upper arms are constituted by the U phase, V phase and W phase and the lower arms are constituted by the X phase, Y phase and Z phase.
In FIG. 2, the lower arm conductor 26 and the three-phase output conductor 27 are constituted by the same conductor. In addition, a negative electrode conductor 28 that connects the negative electrode terminal 31 with the IGBTs 172A to 172D and the diodes 182A to 182B arranged on the lower arm conductor 26 is arranged between the upper arm conductor 25 and the lower arm conductor 26. Electrical connection is effected by means of wire bonding 29 between the respective conductors and the IGBTs and diodes.
In the inverter device shown in FIG. 1 to FIG. 2 the IGBTs 171A to 171D and the diodes 181A to 181C bonded with the conductor 20 and/or upper arm conductor 25 and lower arm conductor 26 are directly connected with a cooler 22 using insulating resin sheet 23, so the thermal resistance of the IGBTs and diode chips within the interior of the power semiconductor element is reduced. Furthermore, since the IGBTs 171A to 171D and diodes 181A to 181C are bonded with the conductor 20 and/or upper arm conductor 25 and lower arm conductor 26 of thickness between 1.5 mm and 5 mm, the thermal time constant becomes large, due to the effect of the thermal capacity of the conductor 20 and/or upper arm conductor 25 and lower arm conductor 26, with the result that transient thermal resistance become small and the rise in temperature during start-up of the inverter becomes small. Cooling efficiency is therefore improved and miniaturization of the inverter device can be achieved.
However, with the conventional inverter device, although the thermal resistance of the IGBTs and the diode chips in the interior of the power semiconductor elements was reduced, there were the following problems.
First of all, manufacturing time was prolonged since considerable time was required to provide the plurality of wire bonding locations involved in the electrical wiring of the plurality of parallel-connected IGBTs or diode chips by wire bonding.
Also, there were structural limits to the extent to which the cooling efficiency could be improved.
Accordingly, one object of the present invention is to provide a novel inverter device and method of manufacturing the device thereof and an electric automobile incorporating this inverter device wherein power semiconductor elements, that provide excellent manufacturing characteristics, are employed, in order to improve current capacity and reduce the size of the inverter device, but wherein the cooling efficiency of the power semiconductor elements is further improved.